Which is better for outdoor wood furniture-urethane or polyurethane?

Urethane is added to many products to protect color, from light and moisture. It also is used in shingles, rubber (tires)(flashing) , plastics etc. Its used in making polyurethane.. Straight urethane dries fast and stays flexible, Tough to work with. For unpainted outdoor wood I use at least three coats of water based polyurethane, marine varnish, shellac, or tung oil depending on the application of the wood. Thompson's Water seal on unstained decks.

I would recommend marine varnish which probably hold up better outside.

urethane and polyurethane are almost identical. They will both crack outdoors from expansion and contraction. Won't even last the summer before cracking. Use a good marine varnish, oil based. Urethane could be used but I sure wouldn't. Polyurethane has no give to it and will crack quickly. You can use water based if you can find it in marine varnish. Talk to the professionals first. That is there business. Read and Follow ALL directions for a good job.

It's the same thing.

I recommend you polyurethane.

Whatever product you choose make sure it says "non yellowing" on the container.